Wikipedia:Reference desk/Archives/Science/2023 January 31

= January 31 =

Why does the late Holocene Susquehanna mouth look like New England?
If Chesapeake Bay is the drowned valley of the Susquehanna River then why does the river enter so far from the apex and look like a canal instead of the typical drowned river shape of the rest of the area? Sagittarian Milky Way (talk) 07:41, 31 January 2023 (UTC)
 * Sorry, I don't follow your question. Can you clarify?  -- Jayron 32 10:00, 31 January 2023 (UTC)
 * It would be helpful if you linked to an image showing what you refer to, but River engineering, including canalization and channelization, and Dredging could be factors. {The poster formerly known as 87.81.230.195} 90.221.194.253 (talk) 14:39, 31 January 2023 (UTC)
 * There was no river engineering. According to this, "The Susquehanna is so old that the mountains and valleys formed around it, rather than the river shaping the valleys." Abductive  (reasoning) 17:02, 31 January 2023 (UTC)
 * Au contraire, there's considerable engineering in the form of dams along it; consider the Conowingo Dam which lies just a few dozen kilometers from the mouth of the river. Water flow along the Susquehanna (like most east-coast rivers) has been heavily controlled and engineered for well over a century by now.  -- Jayron 32 17:08, 31 January 2023 (UTC)
 * Not in the way User:Sagittarian Milky Way was asking, no straightening. The Susquehanna is not navigable, and it drops steeply, so the linearity is natural. Abductive  (reasoning) 17:15, 31 January 2023 (UTC)
 * Yes, that much is true; the Susquehanna largely follows the course that it has for thousands of years. However, I still am not sure what Sagittarian Milky Way was asking, which is why I asked them to clarify.  I'm still not sure what they mean by "looks like a canal" and "apex" and the terminology they are using.  I have crossed the Susquehanna many times, at a large number of places along its course.  At no point does it look like a canal, IMHO.  I have looked at it many times, and I have looked at a great many canals as well.  The Susquehanna doesn't look particularly like a man-made waterway anywhere I have seen; especially not near the mouth.  The views off of the Millard E. Tydings Memorial Bridge don't look particularly canal-like, nor do the views from the Tidewater Grille in Havre de Grace, Maryland, which has a lovely back deck right on the river.  -- Jayron 32 17:31, 31 January 2023 (UTC)


 * Okay canal is an exaggeration. On Google Maps (not Street View) it resembles some of the river mouths in New England (especially the Thames) more than it resembles most of the Chesapeake Bay and North Carolina Sound estuaries. i.e. it doesn't look like the Potomac or Patapsco estuary. New York Bight says the very tip of this embayment is the New York Bight Apex. I guess if you squint you can sort of see the valley turn left at the last minute so it follows the Susquehanna instead of the Elk or North East River but it sure does look like one of those rivers is where the main vein should come from. Maybe the Delaware once drained there aggrandizing those minor Susquehanna tributaries? Sort of like how Glacial Lake Ontario once augmented the Hudson River discharge making it wider than if the ice age never happened (this Niagara of water also stopped the Hudson from draining through the exact tip of the bay by creating a strait through Statenlong Island). Sagittarian Milky Way (talk) 07:14, 1 February 2023 (UTC)
 * A possible explanation is that it is that the "drowned river" effect runs out at that point. The Chesapeake is not just a drowned river due to sea level rise, it is because of the Chesapeake Bay impact crater. The bolide impact cracked all the limestone underlying the whole area, allowing continuous dissolution of the substrata as water infiltrates. This causes slow and steady subsidence, which may end at the "apex", as you put it, far from the epicenter. Abductive  (reasoning) 10:28, 1 February 2023 (UTC)
 * The reason that the Susquehanna is the main river feeding into the area near the north of the bay (but not the northernmost point; which is arbitrary anyways, the fact that the bay continues north of the mouth of the Susquehanna is meaningless, and the northernmost point is not the "apex" in any meaningful sense), is that the Susquehanna is the river with the largest basin in that area. The rivers that empty in further north are rivers like the Elk River (Maryland), which drains a relatively small area.  Given the size of the wide Susquehanna Valley, it all has to get to the sea somehow, and the Susquehanna is it.  The reason why the mouth is relatively straight and not very estuarine is that the Susquehanna is a relatively fast flowing river (or was before extensive engineering and flood control) given that it changes elevation relatively quickly.  It doesn't really meander.  Before the formation of the Chesapeake Bay, it likely had a proper estuary and delta region near its mouth, but all of that is currently under Hampton Roads now.  -- Jayron 32 17:36, 1 February 2023 (UTC)
 * Interesting. The estuariness also peters out on the Carolina coast at about the same distance from the crater, maybe not a coincidence. Sagittarian Milky Way (talk) 20:12, 1 February 2023 (UTC)
 * The Carolina Coast is very estuarine. Much of the sounds inside of the Outer Banks is marshy, brackish, and otherwise perfectly typical of an estuary.  The mouths of places like the Neuse River and the Tar/Pamlico River and places like that are as typically estuary as you are going to find.  The Neuse has a 40 mile long tidal estuary system that starts at about New Bern and continues to the main body of the Pamlico Sound; a similar geography exists on the Tar/Pamlico starting at about Little Washington, and on the Roanoke/Chowan rivers before they reach the Albemarle, etc.  The Carolina coast is very different from what you describe.  -- Jayron 32 12:43, 2 February 2023 (UTC)
 * The Fall line is probably relevant too. While the Susquehanna doesn't have a distinct break with an attendant city the way the Potomac and dozens of other rivers along the East Coast have, it has a fast, steady fall from Harrisburg to the bay that would tend to keep it straight if no other geological processes interfere. The Susquehanna spreads its falls along the whole stretch, is quite shallow and wide, and has many small rapids or riffles instead of one big drop. It is very un-canal-like.   Acroterion   (talk)   12:55, 2 February 2023 (UTC)
 * Contrast the Hudson River, most of which below Albany is a glacial fjord, very deep, and tidal to Albany. There was no glacial influence for the Susquehanna, which is not navigable to any significant extent.  Acroterion   (talk)   13:00, 2 February 2023 (UTC)
 * PART of the Carolina coast is very estuarine. After awhile it starts getting less estuarine though some is unavoidable as the Atlantic Coastal Plain is very flat. Myrtle Beach looks very different from Pamlico Sound on a road map. Sagittarian Milky Way (talk) 17:31, 2 February 2023 (UTC)
 * The river mouths of places in South Carolina look pretty much exactly like the places I described above if you are, you know, standing there looking at it. Myrtle Beach doesn't because Myrtle Beach is not a river outlet; there is none there.  Go to Georgetown, South Carolina, and the mouth of the Pee Dee River is surrounded by the kind of brackish water marshlands you find in estuaries.  That's the first river mouth you find in South Carolina.   You would know that if you go to Georgetown and look around.  You keep saying things which are wrong, and then trying to qualify your wrongness by saying more wrong things.  Please stop that.  -- Jayron 32 12:01, 3 February 2023 (UTC)
 * Sure if I ever stand there (I bet it's idyllic right before the extra bad South-only dew points and pest species start) it'd look like a similar mouth in "NC lagoon" probably all the way to the horizon in every direction (which is as little as 3-3.5 miles). But instead of assuming I can't tell the difference between X and opposite X and nitpicking language it seems obvious I must've always been referring to some aspect of the south Carolinas coast that's different from the bigger, wider indentations further north. Probably the bigger, wider indentations! I always wondered why Delaware Bay, Chesapeake Bay and some NC things like Ablemarle are bigger and wider than anything in SC, GA or East FL ds and who knows maybe it's an asteroid cracking limestone. Sagittarian Milky Way (talk) 20:52, 3 February 2023 (UTC)
 * So, what happened in SC is that Barrier island migration has caused the former barrier islands to basically collide with the land; that's what a mainland beach is. The Grand Strand around Myrtle Beach was, thousands of years ago, a barrier island system that migrated shoreward and ran into the mainland.  It would have looked more like the Outer Banks back then.  Further northward, you can also see this process happening along the Eastern Shore of Maryland and Virginia, where the sound is very narrow, and the barrier islands (Fenwick Island, Assateague Island, Chincoteague Island), where they are much closer to shore than they are in NC, but still further out than SC.  -- Jayron 32 14:05, 6 February 2023 (UTC)